Tag Archives: Rothamsted Insect Survey

I have had an unexpectedly busy couple of weeks talking about declines in insect populations. Back in November of last year I wrote a blog about the sudden media interest in “Insect Armageddon” and followed this up with a more formal Editorial in Annals of Applied Biology at the beginning of the year (Leather, 2018). I mused at the time if this was yet another media ‘storm in a teacup’ but it seems that the subject is still attracting attention. I appeared on television as part of TRT World’s Roundtable programme and was quoted quite extensively in The Observer newspaper on Sunday last talking about insect declines since my student days 🙂 At the same time, as befits something that has been billed as being global, a similar story, featuring another veteran entomologist appeared in the New Zealand press.

The TV discussion was quite interesting, the panel included Nick Rau from Friends of the Earth, Lutfi Radwan, an academic turned organic farmer, Manu Saunders from Ecology is Not a Dirty Word and me. If they had hoped for a heated argument they were out of luck, we were all pretty much in agreement; yes insects did not seem to be as abundant as they had once been, and this was almost certainly a result of anthropogenic factors, intensive agriculture, urbanisation and to a lesser extent climate change. Unlike some commentators who firmly point the finger at the use of pesticides as the major cause of the declines reported, we were more inclined to towards the idea of habitat degradation, fragmentation and loss. We also agreed that a big problem is a lack of connection with Nature by large sections of the population, and not just those under twenty. We also felt very strongly that governments should be investing much more into research in this area and that we desperately need more properly replicated and designed long-term studies to monitor the undeniable changes that are occurring. I had, in my Editorial and an earlier blog post, mentioned this point and lamented the paucity of such information, so was pleasantly surprised, to receive a couple of papers from Sebastian Schuh documenting long-term declines in Hemiptera and Orthoptera in Germany (Schuh et al., 2012ab), although of course sad, to see yet more evidence for decreasing insect populations.

The idea that insects are in terminal decline has been rumbling on for some time; more than a decade ago Kelvin Conrad and colleagues highlighted a rapid decline in moth numbers (Conrad et al., 2006) and a few years later, Dave Brooks and colleagues using data from the UK Environmental Change Network revealed a disturbing decline in the numbers of carabid beetles across the UK (Brooks et al., 2012). In the same year (2012) I was asked to give a talk at a conference organised by the Society of Chemical Industry. Then, as now, I felt that pesticides were not the only factor causing the biodiversity crisis, but that agricultural intensification, habitat loss and habitat degradation were and are probably more to blame. In response to this quote in the media at the time:

“British Insects in Decline

Scientists are warning of a potential ecological disaster following the discovery that Britain has lost around 7% of its indigenous insect species in just under 100 years.

A comparison with figures collected in 1904 have revealed that around 400 species are now extinct, including the black-veined white butterfly, not seen since 1912, the Essex emerald moth and the short-haired bumblebee. Many others are endangered, including the large garden bumblebee, the Fen Raft spider, which is only to be found in a reserve on the Norfolk/Suffolk border, and the once common scarlet malachite beetle, now restricted to just three sites.

Changes to the insects’ natural habitats have been responsible for this disastrous decline in numbers. From housing and industrial developments to single-crop farming methods, Britain’s countryside has become increasingly inhospitable to its native insects.”

I chose to talk about “Forest and woodland insects: Down and out or on the up?” I used data from that most valuable of data sets, the Rothamsted Insect Survey to illustrate my hypothesis that those insects associated with trees were either doing better or not declining, because of increased tree planting over the last fifty years. As you can see from the slides from my talk, this does indeed seem to be the case with moths and aphids that feed on trees or live in their shade. I also showed that the populations of the same species in northern Britain, where agriculture is less intensive and forests and woodlands more prevalent were definitely on the up, and this phenomenon was not just confined to moths and aphids.

Two tree aphids, one Drepanosiphum platanoidis lives on sycamore, the other Elatobium abietinum, lives on spruce trees; both are doing rather well.

Two more tree-dwelling aphids, one on European lime, the other on sycamore and maples, both doing very well. For those of you unfamiliar with UK geography, East Craigs is in Scotland and Newcastle in the North East of England, Hereford in the middle and to the west, and Starcross in the South West, Sites 2, 1, 6 and 9 in the map in the preceding figure.

Two conifer feeding moth species showing no signs of decline.

On the up, two species, a beetle, Agrilus biguttatus perhaps due to climate change, and a butterfly, the Speckled Wood Pararge aegeria, due to habitat expansion and climate change?

It is important however, to remember that insect populations are not static, they vary from year to year, and the natural fluctuations in their populations can be large and, as in the case of the Orange ladybird, Halyzia sedecimguttata, take place over a several years, which is yet another reason that we need long-term data sets.

It is obvious, whether we believe that an ecological catastrophe is heading our way or not, that humans are having a marked effect on the biodiversity that keeps our planet in good working order and not just through our need to feed an ever-increasing population. A number of recent studies have shown that our fixation with car ownership is killing billions of insects every year (Skórka et al., 2013; Baxter-Gilbert et al.,2015; Keilsohn et al., 2018) and that our fear of the dark is putting insects and the animals that feed on them at risk (Eccard et al., 2018; Grubisic et al., 2018). We have a lot to answer for and this is exacerbated by our growing disconnect from Nature and the insidious effect of “shifting baselines” which mean that succeeding generations tend to accept what they see as normal (Leather & Quicke, 2010, Soga & Gaston, 2018) and highlights the very real need for robust long-term data to counteract this dangerous and potentially lethal, World view (Schuh, 2012; Soga & Gaston, 2018). Perhaps if research funding over the last thirty years or so had been targeted at the many million little things that run the World and not the handful of vertebrates that rely on them (Leather, 2009), we would not be in such a dangerous place?

I am, however, determined to remain hopeful. As a result of the article in The Observer, I received an email from a gentleman called Glyn Brown, who uses art to hopefully, do something about shifting baselines. This is his philosophy in his own words and pictures.

I have been musing about extinctions and shifting baselines for a while now; BREXIT and an article by Simon Barnes in the Sunday Times magazine (3rd September 2016) finally prompted me to actually put fingers to keyboard. I fear that BREXIT will result in even more environmental damage than our successive governments have caused already. They have done a pretty good job of ignoring environmental issues and scientific advice (badgers) even when ‘hindered’ by what they have considered restrictive European legislation and now that we head into BREXIT with a government not renowned for its care for the environment I become increasing fearful for the environment. Remember who it was who restructured English Nature into the now fairly toothless Natural England, because they didn’t like the advice they were being given and whose government was it who, rather than keep beaches up to Blue Flag standard decided to reclassify long-established resort beaches as not officially designated swimming beaches? And, just to add this list of atrocities against the environment, we now see our precious ‘green belt’ being attacked.

My generation is liable to wax lyrical about the clouds of butterflies that surrounded us as we played very non PC cowboys and Indians outside with our friends in the glorious sunshine. We can also fondly reminisce about the hordes of moths that used to commit suicide in the lamp fittings or beat fruitlessly against the sitting room windows at night. The emptying of the lamp bowl was a weekly ceremony in our house. We also remember, less fondly, having to earn our pocket-money by cleaning our father’s cars, laboriously scraping the smeared bodies of small flies from windscreens, headlamps and radiator grilles on a Saturday morning. A few years later as students, those of us lucky enough to own a car, remember the hard to wash away red smears left by the eyes of countless Bibionid (St Mark’s) flies, as they crashed into our windscreens.

Are these memories real or are we looking back at the past through those rose-tinted glasses that only show the sunny days when we lounged on grassy banks listening to In the Summertime and blank out the days we were confined to the sitting room table playing board games?

We have reliable and robust long-term data sets showing the declines of butterflies and moths over the last half-century or so (Thomas, 2005; Fox, 2013) and stories about this worrying trend attract a lot of media attention. On a less scientific note, I certainly do not find myself sweeping up piles of dead moths from around bedside lamps or extricating them from the many spider webs that decorate our house. Other charismatic groups, such as the dragonflies and damselflies are also in decline (Clausnitzer et al., 2009) as are the ubiquitous, and equally charismatic ground beetles (carabids) (Brooks et al., 2012). But what about other insects, are they too on the way out? A remarkable 42-year data set looking at the invertebrates found in cereal fields in southern England (Ewald et al., 2015) found that of the 26 invertebrate taxa studied less than half showed a decrease in abundance; e.g. spiders, Braconid parasitic wasps, carabid beetles, Tachyporus beetles, Enicmus (scavenger beetles), Cryptophagid fungus beetles, leaf mining flies (Agromyzids), Drosophila, Lonchopteridae (pointed wing flies), and surprisingly, or perhaps not, aphids. The others showed no consistent patterns although bugs, excluding aphids, increased over the study period. Cereal fields are of course not a natural habitat and are intensely managed, with various pesticides being applied, so are perhaps not likely to be the most biodiverse or representative habitats to be found in the UK.

But what about the car-smearing insects, the flies, aphids and other flying insects? Have they declined as dramatically? My first thought was that I certainly don’t ‘collect’ as many insects on my car as I used to, but is there any concrete evidence to support the idea of a decline in their abundance. After all, there has been a big change in the shape of cars since the 1970s.

Top row – cars from 1970, including the classic Morris 1000 Traveller that my Dad owned and I had to wash on Saturdays.

Bottom row the cars of today, sleek rounded and all looking the same.

Cars were much more angular then, than they are now, so perhaps the aerodynamics of today’s cars filter the insects away from the windscreen to safety? But how do you test that? Then I remembered that the RSPB had once run a survey to address this very point. Sure enough I found it on the internet, the Big Bug Count 2004, organised by the RSPB. I was very surprised to find that it happened more than a decade ago, I hadn’t thought it was that long ago, but that is what age does to you 🙂

The “Splatometer” as designed by the RSPB

The idea, which was quite cool, was to get standardised counts of insect impacts on car number plates. The results were thought to be very low as the quote below shows, but on what evidence was this based?

“Using a cardboard counting-grid dubbed the “splatometer”, they recorded 324,814 “splats”, an average of only one squashed insect every five miles. In the summers of 30-odd years ago, car bonnets and windscreens would quickly become encrusted with tiny bodies.” “Many people were astonished by how few insects they splatted,” the survey’s co-ordinator Richard Bashford, said.

Unfortunately despite the wide reporting in the press at the time, the RSPB did not repeat the exercise. A great shame, as their Big Garden Birdwatch is very successful and gathers useful data. So what scientific evidence do we have for a decline in these less charismatic insects? Almost a hundred years ago, Bibionid flies were regarded as a major pest (Morris, 1921) and forty years ago it was possible to catch almost 70 000 adults in a four week period from one field in southern England (Darcy-Burt & Blackshaw, 1987). Both these observations suggest that in the past Bibionids were very common. It is still possible to pluck adult Bibionids out of the air (they are very slow, clumsy fliers) in Spring, but if asked I would definitely say that they are not as common as they were when I was a student. But as Deming once said, “Without data, you’re just another person with an opinion.” In the UK we are fortunate that a long-term source of insect data exists, courtesy of Rothamsted Research, the longest running agricultural research station in the world. Data have been collected from a nationwide network of suction and light traps for more than 50 years (Storkey et al., 2016). Most of the publications arising from the survey have tended to focus on aphids (Bell et al., 2015) and moths (Conrad et al., 2004), although the traps, do of course, catch many other types of insect (Knowler et al., 2016). Fortuitously, since I was interested in the Bibionids I came across a paper that dealt with them, and other insects likely to make an impact on cars and splatometers (Shortall et al., 2009). The only downside of their paper was that they only looked at data from four of the Rothamsted Suction Traps, all from the southern part of the UK, which was a little disappointing.

Location and results of the suction traps analysed by Shortall et al. (2009).

Only three of the trap showed downward trends in insect biomass over the 30 years (1973-2002) analysed of which only the Hereford trap showed a significant decline. So we are really none the wiser; the two studies that focus on a wider range of insect groups (Shortall et al., 2009; Ewald et al., 2015) do not give us a clear indication of insect decline. On the other hand, both studies are limited in their geographic coverage; we do not know how representative the results are of the whole country.

What a shame the RSPB stopped collecting ‘splatometer’ data, we would now have a half-decent time series on which to back-up or contradict our memories of those buzzing summers of the past.

Post script

After posting this I came across this paper based on Canadian research which shows that many pollinators, possibly billions are killed by vehicles every year. This reduction in insect numbers and biomass has also been reported in Germany.

The previous papers in this series (Southwood, 1961; Haukioja & Niemelä 1976; Owen & Weigert, 1976), were all ones that had an influence on my post-PhD career. This one in contrast, had a direct effect on my PhD as well as on my subsequent career, and was, I guess, greatly influential in the publication of the first book to deal with the ecology of insect overwintering (Leather, Walters & Bale, 1993). In 1964 Mike Way, one of the early proponents of Integrated Pest Management (in fact considered to be the father of UK IPM), was working on control methods for the black bean aphid, Aphis fabae.

Mike had recently joined Imperial College from Rothamsted Research Station where he had been leading research on ways to reduce pesticide use by farmers and growers. During his time at Rothamsted he had worked closely with a colleague, C.J. Banks on the black bean aphid including studies on the overwintering eggs. As they said in the introduction to their paper, published four years after their experiments; “During the British winter A. fabae survives almost exclusively in the egg stage. Egg mortality might therefore be important in affecting size of populations of this species and in predicting outbreaks”. They investigated the effects of temperature and predators on the mortality of the eggs on the primary host, spindle, Euonymus europaeus, and concluded that the levels of mortality seen would not affect the success of the aphids the following spring. By 1968 (Way & Banks, 1968) they had followed up on the idea and began to feel confident that aphid populations on field beans could be predicted from the number of eggs on the winter host; spindle bushes. The publication of this paper stimulated the setting up of a long-term collaborative project monitoring Aphis fabae eggs on spindle bushes at over 300 locations throughout England south of the River Humber, and monitoring aphid numbers in about 100 bean fields per year. In 1977 the results were finally published (Way et al., 1977) and the highly successful black bean aphid forecasting system was born. This was further refined by using the Rothamsted aphid suction trap data (Way et al., 1981).

This was also the year that I began my PhD at the University of East Anglia, working on the bird cherry-oat aphid, Rhopalosiphum padi. In the course of my preparatory reading I came across Way & Banks (1964) just in time to set up a plot of bird cherry saplings which I monitored for the next three winters, the first winter’s work resulting in my first publication (Leather, 1980). I subsequently went on to develop the bird cherry aphid forecasting system still used in Finland today (Leather & Lehti, 1981; Leather, 1983; Kurppa, 1989).

Sadly, despite the great success of these two systems there has not been a huge take-up of the idea, although the concept has been looked at for predicting pea aphid numbers in Sweden (Bommarco & Ekbom, 1995) and rosy apple aphids in Switzerland (Graf et al., 2006). Nevertheless, for me this paper was hugely influential and resulted in me counting aphid eggs for over 30 years!

Michael Way died in 2011 and is greatly missed by all those who knew him well. He examined my PhD thesis, and to my delight and relief, was very complimentary about it and passed it without the need for corrections. I was greatly honoured that a decade or so later I became one of his colleagues and worked alongside him at Silwood Park. He was a very modest and self-deprecating man and never had a bad word to say about anyone. He had a remarkable career, his first paper published in 1948 dealing the effect of DDT on bees (Way & Synge, 1948) and his last paper published in 2011 dealing with ants and biological control (Seguni et al., 2011), a remarkable 63 year span. His obituary can be found here http://www.telegraph.co.uk/news/obituaries/science-obituaries/8427667/Michael-Way.html

I think that even those of us who are not entomologists are familiar with the attraction that insects, particularly moths, have for light. The great Sufi philosopher Bahauddin Valad (1152-1231) wrote the following lines

It may thus come as a bit of surprise to realise that ‘modern’ entomologists were quite slow to develop bespoke traps that took advantage of this aspect of insect behaviour. That said, according to Beavis (1995) the Roman author Columella (Lucius Junius Moderatus, 4-7 AD), describes a light trap to be used to protect bee hives from wax moth attacks. A pretty much identical trap was still being used in 1565 (Gardiner, 1995) although he erroneously calls it the first light-trap. As far as I can tell the early ‘modern’ Lepidopterists used the white sheet technique, still used today, where a light source such as a paraffin lamp (nowadays an electric light or powerful torch) was suspended above or behind a white sheet, from which the intrepid entomologist collected specimens of interest that come to rest on the sheet. This can be very efficient but does require the entomologist to be ‘on duty’ throughout the trapping

The white sheet technique.

period, although on a fine night, with good companionship and an ample supply of beer, or other alcoholic beverage, it can be a very pleasant way to spend a long evening 😉

The earliest published reference to a modern bespoke light trap that I have been able to find is a patent from 1847 for a modified beehive which includes a light trap to lure wax moths away from the main part of the hive (Oliver Reynolds, 184, US Patent5211; http://www.google.com/patents/US5211).

The modified Reynolds Beehive incorporating moth trap.

The second published reference to a bespoke light trap is again one designed to control wax moths and is described in a patent application by J M Heard dated 1860. In this case as far as I can make out the lamp is actually glass coated with a phosphorescent material rather than using a candle or oil flame.

“The basin A, is supplied with a requisite quantity of molasses or other suitable substance to serve as a bait, and the inner sides of the glass plates c, of the lamp C, are covered with a mixture of phosphorus and oil or phosphorus combined with any suitable substance to form a cement, or a stick E, may be coated with the cement, said stick being passed through the tube e, into the lamp, as shown plainly in Fig. 1. The insects decoyed by the light and attracted by the bait, strike against the inclined glass plates c, and fall into the basin A. By having the plates c, inclined the insects are made to fall through the opening b, into the basin and said opening is permitted to be comparatively small and the cover a, of the basin in connection with the cover D, of lamp protect perfectly the bait from sun and rain, thereby protecting an unnecessary waste of the same. During the day the phosphorus of course is not needed unless it be cloudy, but the device is chiefly efficacious at night as the visits of the insects are mostly nocturnal.”

So whilst beekeepers and agriculturalists were busy using traps to attract moths to kill them what were the lepidopterists doing? It appears that they were using whole rooms as light traps as described here by H T Stainton in 1848.

A later Victorian entomological ‘how to’ book, added instructions of how to use gas and paraffin lamps outside, with the lepidopterist standing ready with his net (Greene, 1880).

The 20th Century was however, when we see the birth of the light traps as we know them today. First on the scene was the Rothamsted Trap, developed by the great C B Williams, which was

The electric ‘fixed’ Rothamsted Trap.

The ‘portable’ Rothamsted Trap – Williams (1948)

developed from earlier versions that he used in the 1920s and 1930s, in Egypt and England (Williams, 1924, 1935).

Rothamsted trap in action

Apparently the first electrical light trap to use an ultra-violet light was made in 1938 (Barratt, 1989) and used in the 1940s (Fry & Waring, 2001) but it was not until 1950 that the first commercially available version was produced (Robinson & Robinson, 1950).

The Robinson Trap – very popular and ideal for use in gardens where there is easy access to a mains supply.

Strangely, considering that the Americans had been first on the scene with patented light traps it was not until 1957 that the Pennsylvanian and Texas traps appeared on the scene (Frost, 1957) closely followed by the Texas traps (Hollingsworth et al., 1963). These traps used fluorescent tubes instead of bulbs and were particularly good at catching beetles, moths and ants. The Texas trap and the Pennsylvania trap were essentially the same, the main difference being that the Pennsylvania trap has a circular roof to prevent train entering the killing bottle. As Southwood (1966) somewhat tongue in cheek says, this may reflect the differences in the climate of the two states 😉

The Pennsylvanian Light Trap.

In the 1960s the Heath Trap appeared on the scene (Heath, 1965). This was billed as being extremely portable, being able to be carried in a back pack and also able to be run either from a mains supply or from a 12 volt battery.

The Heath Light trap.

Less expensive and more portable is the Skinner trap, (designed by Bernard Skinner in as far as I can make out in the early 1980s, please let me know if you know exactly) which comes in wooden and aluminium versions and is collapsible, so that if needed, several can be transported at once. It comes in both mains and battery versions.

The Skinner light trap – relatively inexpensive and very portable.

An interesting combination of light and odour being used to attract and trap insects, in this case to ‘control’ them, is the Strube Stink bug trap. This is an American invention and is used to protect US householders against the the Brown Marmorated Stink Bug, Halyomorphahalys, an invasive species from Asia which appears to have developed a propensity to overwinter in people’s houses. I remember a few years ago that we in the UK were warned that it might cross the channel from France; this resulted in lurid headlines in the ‘Red Top’ newspapers with wording like ‘stench spraying insect’ being used 😉

Robinson, H.S. & Robinson, P.J.M. (1950) Some notes on the observed behaviour of Lepidoptera in the vicinity of light sources together with a description of a light trap designed to take entomological samples. Entomologist’s Gazette, 1, 3-20

Southwood, T.R.E. (1966) Ecological Methods. Chapman & Hall, London

Stainton, H.T. (1848) On the method of attracting Lepidoptera by light. The Zoologist, 6, 2030-2031

There are of course more light traps out there, many being variations of those described above, or for specific insect groups such as mosquitoes or aquatic traps for Cladocera (water fleas). Many ‘home made’ traps also exist, such as the ‘portable’ one I made for use on the field course that I used to run at Silwood Park.

The Leather Light Trap

I used a rechargeable battery lantern, but other light sources would also work. In retrospect I should have painted the Perspex black so that only the ‘entrance’ funnels emitted light. There was a tendency for insects to sit on the outside of the trap rather than enter it.

I write about politics, nature + the environment. Some posts are serious, some not. These are my views, I don't do any promotional stuff and these views are not being expressed for anyone who employs me.

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